Hook and chain assemblies are well known for their use in lifting, towing, and/or restraining cargo, often particularly of heavy weight. It is well known in the art that hook and chain assemblies include a throat that will accept one link from the chain. Various techniques have been proposed to prevent the sliding of the chain through the throat that would cause the cargo to fall at a great risk of injury or death to the workers, and damage to the cargo. The present applicant, in U.S. Pat. No. 5,362,117, found one way to solve the problem by devising a hook with a retractable, spring-loaded lock pin that retains the chain link placed in the throat. This spring-loaded lock-pin included a hook body having a throat; a lock-pin having a link retainer located within a hole produced in the hook body; a spring retainer extending from the link retainer; a biasing mechanism for biasing the lock-pin in a retracted position in the hole and locking means including a roll pin to lock positively the lock-pin in a retaining position.
The applicant's previous invention works reasonably well as an effective, yet inexpensive, design to provide a safety lock for a grab hook. The applicant has discovered that, although the previously patented apparatus is effective, there are nonetheless some drawbacks. The spring retainer may lose tension from repeated use. The lock pin and/or roll pin can be damaged. More importantly, the recess hole in the hook body reduces the usable portion of the U-shaped throat, limiting the range of the diameter of chain links that can be utilized. This recess hole in the hook can weaken its structure, and requires an additional step of manufacture. The locking mechanism is not easily adapted to be used with existing grab hooks already on the market. The locking/unlocking means can also be cumbersome to lock and unlock and may not be performed on either side of the hook.
It is therefore an object of the present invention to overcome all of the above-mentioned disadvantages of prior art locks for grab hooks.